A. Field of the Invention
The present invention is related to a damper assembly that dampens and absorbs vibrations while transmitting torque from an input rotor to an output rotor and in particular, to a damper assembly having a plate-shaped intermediate member disposed between two or more elastic members.
B. Description of the Related Art
Ordinarily, a damper assembly dampens and absorbs vibrations transmitted to an output rotor from an input rotor while transmitting torque from the input rotor to the output rotor. A damper (hereinafter referred to as a lockup damper) that includes a lockup mechanism disposed inside a torque converter is an example of this type of damper assembly.
A torque converter is a mechanism having three types of impellers (impeller, turbine, and stator) housed internally and uses hydraulic fluid (also contained internally) to transfer torque. The impeller is secured to a front cover into which torque is inputted. Fluid moving from the impeller moves toward the turbine thereby transferring torque to the turbine from the impeller. The turbine is connected to a main drive shaft of a transmission.
The lockup mechanism is disposed between the front cover (input rotor) and the turbine (output rotor) and is a device that mechanically couples the front cover and the turbine to directly transmit torque bypassing the hydraulic fluid.
Normally, the lockup mechanism includes a piston member that can be selectively engaged with the front cover in response to fluid pressure changes inside portions of the torque converter. A drive member is secured to the piston member. A coil spring is supported on the drive member, and a driven member is elastically coupled to the piston member in the direction of rotation by means of the coil spring. The driven member is secured to the turbine. The members that constitute the lockup mechanisms are lockup dampers that absorb and dampen the vibrations transmitted to the torque converter, and in particular, the lockup dampers absorb vibration when the lockup clutch is engaged.
When the lockup mechanism operates, the piston member slides on or is pressed against the front cover. The torque is then transmitted from the front cover to the piston member and then is further transferred to the turbine through the coil spring. At this time, the lockup mechanism transmits torque together with absorbing and dampening twisting vibrations caused by the engagement and movement of portions of the lockup damper. Hereupon, by means of repeatedly compressing the coil spring between the drive member and the driven member, twisting vibrations are absorbed and dampened.
Recently, there have been many configurations in which a lockup damper disposed at an outer radial portion within a torque converter. Such a lockup damper includes a coil spring. The outer radial portion of the torque converter is a desirable location for such a damper because a comparatively large clearance results such that the overall dimensions in the axial direction of the torque converter can be reduced. However, if the coil spring is disposed at the outer radial portion of the torque converter, the total displacement angle of the lockup damper is smaller when compared with damper mechanisms that have a coil spring disposed in a radial intermediate portion within the torque converter. Namely, if a coil spring with the same dimensions is simply moved to the outer radial portion, the angle of relative rotary displacement between the input rotor and the output rotor can rotate becomes smaller because of the increased distance away from the center of the relatively rotating members of the lockup damper. As a result, the total relative rotary displacement is reduced narrowing and reducing the dampening characteristics of the lockup damper thus reducing the vibration absorption properties of the damper mechanism in a low revolution region (low RPM) of an engine.
As a method to eliminate this dis-advantage, arranging two or more coil springs in series through an intermediate member is considered. In other words, coupling two or more coil springs in series by providing an intermediate member that has a portion that supports the ends of the coil springs. By means of this, the dimensions of the coil springs coupled in series that can be compressed increases thereby making it possible to ensure a relatively large relative rotary displacement angle. Further, if two coil springs with different spring constants are combined in series, it becomes possible to improve the twisting characteristics of the lockup damper by means of having two characteristic levels.
However, in order to use two springs in series with an intermediate member, it becomes necessary to increase the size of the lockup damper and complicate the shape of other elated elements in order to avoid interference between the various elements of the lockup damper and the torque converter. In an effort to control undesirable condition associated with the use of two springs, an intermediate member has been proposed that is made from a plate material with a small plate thickness in comparison to the diameter of the coil spring, as shown by the intermediate member 94 in FIG. 6 and FIG. 7.
However, the intermediate member 94 functions to support the end of both coil springs 97 and 98. The contact surface area between the plate material with a plate thickness (t1) of this supporting portion 94a and the end s of the coil springs 97 and 98 becomes smaller making it difficult to provide a stable support because of problems which include precision of the dimensions. In other words, if the balance of the support of the ends of the coil springs 97 and 98 is lowered due to the thickness (t1) of the plate material only, a state will occur in which rotation of the ends of the coil springs 97 and 98 will be allowed and as shown in FIG. 8 for example, there is a possibility that the coil spring 98 may bend when the coil string 98 is compressed. Because of this, the design had to take into account compression buckling of the coil springs causing deviations in the damper characteristics and the action of excessive stress on the coil springs. Moreover, if the coil springs are in a bent state, sliding will occur between the coil springs and other members which also creates the danger of degenerating damper characteristics.